Binding to an actin subunit and promoting its dissociation from an actin filament by a local change in actin subunit conformation and orientation, and severing of filaments. [ http://www.ncbi.nlm.nih.gov/pubmed/23395798 http://www.ncbi.nlm.nih.gov/pubmed/23727096 http://www.ncbi.nlm.nih.gov/pubmed/11812157 ]